The present invention relates to an improved thermosensitive recording material comprising a thermosensitive layer comprising a colorless or light-colored coloring compound and a developer capable of coloring the coloring compound by reacting therewith, upon application of heat thereto, and a support member for supporting the thermosensitive layer thereon, which thermosensitive recording material is improved so as to form a color with high density by application of a relatively small quantity of heat thereto, without the problems of discoloration by pressure or friction, and without deterioration during storage, and which does not contribute to the accumulation of dust on a thermal head during an image recording process by use of a thermal printer with a thermal head.
Conventionally, a thermosensitive recording material comprises a support member, for example, paper, synthesized paper or a resin film, and a thermosensitive layer formed thereon capable of forming a color upon application of heat thereto. For the application of heat, for example, a thermal printer with a thermal head is employed. In the thermosensitive layer, there are contained a colorless or light-colored leuco dye with a lactone ring, a lactam ring or a spiro-pyran ring as a coloring compound, and an acidic material as a developer for coloring the coloring compound by the reaction therewith, upon application of heat thereto.
As compared with other conventional recording materials, thermosensitive recording materials of the above-described type have advantages in that recording can be performed without requiring complicated steps such as development and image fixing; therefore, such recording is done speedily, quietly and at a low cost. Because of these advantages, there is a great demand for a thermosensitive recording material that is suitable for use in high speed recording, in particular, for use with computers, facsimile machines and a variety of measuring instruments.
For the above-mentioned objects, it is preferable that thermosensitive recording materials have the following properties:
(1) A color with high density in sharp contrast with the background can be formed by application of a relatively small quantity of energy thereto;
(2) There is no discoloration of the recording material by pressure or friction, whereby it is possible to obtain clear images with high image density;
(3) The recording material can be stored for a long period of time, without deterioration including fogging during the period of storage; and
(4) The recording material does not substantially contribute to the accumulation of dust on a thermal head during an image recording process by use of a thermal printer with a thermal head, thereby attaining a smooth thermal recording operation, including scanning by the head over an extended period of time.
In an attempt to obtain a thermosensitive recording material with the above-described properties, there has been proposed a thermosensitive recording material which contains a fluoran compound of the following formula as a coloring compound; a conventional acidic material as a developer; and stearic acid amide as an auxiliary agent: ##STR3##
This conventional thermosensitive recording material yields, in fact, clearer images than other conventional thermosensitive recording materials do. However, it is not improved with respect to (i) the formation of a color with high image density such as can be employed for high speed recording process; (ii) discoloration by pressure or friction; (iii) deterioration, including fogging, during storage; and (iv) accumulation of dust on a thermal head during an image recording process when a thermal printer with a thermal head is employed.